As personal computers, workstations, and the like have become widespread in recent years, a large amount of research has been conducted into the magnetic tapes (known as back-up tapes) that are employed as external recording media for recording computer data. In the development of magnetic tapes for such uses, particularly as computers have decreased in size and increased in information processing capability, there has been a strong demand for increased recording capability to increase recording capacity and achieve size reduction. In the area of magnetic disks, as well, the rapid development of information technology is spawning a demand for the development of magnetic disks of ever greater density and capacity.
In the magnetic recording media developed thus far, a magnetic layer comprising a ferromagnetic hexagonal ferrite powder in the form of iron oxide, Co-modified iron oxide, or CrO2 dispersed in a binder that is coated on a nonmagnetic support has been widely employed. In these, the use of ferromagnetic metal powder and ferromagnetic hexagonal ferrite powder as magnetic powders is known to afford good high-density recording characteristics. For example, in the case of magnetic disks, 10 MB MF-2TD and 21 MB MF-2SD high-capacity disks employing ferromagnetic metal powder with good high-density recording characteristics are known. High-capacity disks employing ferromagnetic hexagonal ferrite powder in the form of 4 MB MF-2ED and 21 MB flopticals are also known. However, today, with sharp increases in the quantity of data being handled, even these magnetic disks do not afford adequate recording capacity and there is demand for magnetic disks of even greater capacity.
In the field of magnetic tapes, technologies of reducing the layer thickness of magnetic tapes to permit high-density recording are advancing. Numerous magnetic tapes having a magnetic layer thickness of equal to or less than 2 μm have appeared. With the high densification of magnetic recording media, a demand for greater coating smoothness has come, and the trend in magnetic material has been toward microparticles.
However, since the stiffness of the magnetic recording medium is affected by the cube of the thickness, when the thickness of the magnetic layer is reduced, head touch deteriorates and the error rate climbs. In response, techniques have been proposed to compensate for the drop in stiffness by providing an undercoating layer comprising a tabular filler and a binder (See Japanese Patent No. 2,667,040 and Japanese Unexamined Patent Publication (KOKAI) Heisei Nos. 4-119518, 4-195819, 4-364220, 5-46971, and 5-128487). In these techniques, since the tabular filler is thick, the surface properties of the undercoating layer and the magnetic layer are adversely affected, and the error rate increases.
In addition to the problems of the deterioration of electromagnetic characteristics and dropout due to worsening of head touch due to a drop in stiffness, a new problem is generated in the form of a drop in running durability. Further, in the magnetic recording media that are actually employed in digital VRC systems and DDS-4 systems, for example, shifts in the coefficients of temperature and moisture expansion occur during recording and during reproduction, and it is not necessarily possible to obtain good electromagnetic characteristics or durability.
Accordingly, it is an object of the present invention to provide a magnetic recording medium having high C/N, low error rate, and excellent running durability.